Conventional hydraulic closed circuit systems with a single rod type of hydraulic cylinder device as a hydraulic actuator, generally include a low pressure selecting valve (flushing valve) and a charge circuit as well, thereby providing a closed circuit.
The related art described in Patent Document 1 (JP, A 2002-54602) eliminates the need for the low pressure selecting valve (flushing valve) in such a conventional hydraulic closed circuit system by incorporating the following measure as an alternative. That is, this alternative includes: arranging two hydraulic pumps of a bidirectional delivery type as a hydraulic source; connecting one of the hydraulic pumps at its paired delivery ports to a bottom-side port and rod-side port of the hydraulic cylinder device, thereby composing a hydraulic closed circuit; and connecting the other hydraulic pump at one of its paired delivery ports to the bottom-side port of the hydraulic cylinder device and at the other of the paired delivery ports to a tank. The alternative absorbs a difference in a flow rate of a hydraulic fluid between the bottom side and rod side of the hydraulic cylinder device.